Mutations in the parkin gene cause PARK2, a predominantly early-onset autosomal recessive form of Parkinsonism. Parkin mutations are also found in patients with tremor-predominant later onset forms of Parkinson disease (PD) indistinguishable from idiopathic Parkinson's disease. Parkin is an E3 ubiquitin ligase that attaches ubiquitin chains to several proteins destined for degradation through the proteasome-dependent protein degradation pathway. Some proteins that interact with parkin, such as a-synuclein and synphilin-1, have themselves been found to cause Parkinson's disease, when mutated. In previous experiments, we identified two members of the synaptotagmin (syt) family as parkin binders. We have now identified a novel parkin-binding protein with homologies to synapsin, designated synapsin-like-protein (SLP). SLP and synaptotagmin XI are both found in Lewy bodies of PD patients. We will test the following hypotheses: 1) parkin interacts and regulates a select group of synaptic vesicle associated proteins. 2) Genes encoding these proteins contain causative mutations or predisposing sequence variants in patients with familial or sporadic forms of Parkinsonism. Two Specific Aims are proposed: 1) We will further characterize the parkin-SLP interaction, and investigate whether mutant parkins lose the ability to bind SLP or to ubiquitinate SLP. We will determine whether parkin accelerates degradation of SLP. 2) We will explore sequence variants in the SLP, SYT1 and SYT11 genes in two PD patient groups and five matched control groups. We will establish which variants represent rare causative mutations and which variants may constitute susceptibility alleles. Variants will be tested for cell toxicity using an in vitro assay. The ultimate goal of this R21 proposal is to further characterize proteins involved in parkin function and to screen these proteins for mutations or susceptibility alleles in PD patients. [unreadable] [unreadable]